In vitro fertilization (IVF) and embryo culture studies have contributed markedly to our understanding of gamete physiology, infertility and the potential for enhancing reproductive efficiency. Most of our present knowledge about mammalian fertilization and embryo development is derived from a few non-carnivore species. Our plan is to exploit unique reproductive characteristics of the domestic cat and its wild relatives to improve our fundamental understanding of fertilization and embryogenesis. These features are based on previous findings that (i) "normospermic" felids experience high IVF rates, (ii) certain felid species or populations produce many pleiomorphic sperm and (iii), in the domestic cat, even normal-appearing sperm from teratospermic males are compromised in ability to bind and penetrate the zona pellucida (ZP) and to fertilize conspecific oocytes. Methods will include: gamete co-incubation; embryo culture/transfer; corpus luteum histology/hormone-receptor content; electron microscopy; objective measures of sperm morphology and motility; sperm staining; protein electrophoresis and micromanipulation. Experimental variables will include: the developmental kinetics of "natural" versus IVF embryos; the survival of early versus late stage IVF embryos; and sperm factors (ultrastructure, motility/metabolism, ability to achieve the acrosome reaction, binding receptors, ability to penetrate the ZP barrier and interact with the vitellus) that might explain why "normal" sperm from teratospermic males are less capable of fertilization. To clarify mechanisms even further, these strategies will be applied to an array of wild felid species producing different levels and types of teratospermia. This represents the only effort in any carnivore species to comprehensively characterize, integrate and understand the events spanning sperm capacitation to embryo implantation. Especially important are planned studies to assess potential mechanisms by which structurally- normal sperm from teratospermic ejaculates affect gamete interaction and fertilization while identifying the fate of specific sperm pleiomorphisms. Studies of related taxa provide unique opportunities to compare and more readily identify those factors dictating reproductive success within species, populations and individuals. Our findings may provide clues to the significance of sperm pleiomorphisms highly characteristic of human ejaculates and may have practical significance for propagating rare domestic cat models or endangered species.